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Nanotechnology: Should carbon nanotubes be handled in the workplace like asbestos?

Multi-walled carbon nanotubes in conducting airways of the mouse lung after inhalation exposure. By Robert Mercer

Nanotechnology poses a question for occupational health and safety professionals. Does this technology, and the tiny nanoparticles that are its tools, pose an unintended risk of illness or injury for workers employed in the industry?

The National Institute for Occupational Safety and Health is at the forefront of the effort to understand the health and safety ramifications of working with nanomaterials. There have been an increasing number of scientific publications from the research community at large—including a new study issued just this week—that address one type of nanomaterial in particular, carbon nanotubes, and seek to determine if they biologically behave like asbestos. That is, if inhaled, are carbon nanotubes likely to cause irreparable and fatal effects such as those associated with asbestos exposure? The effects of asbestos include severe lung fibrosis or scarring, lung cancer, including cancer of the lining of the lungs or pleura called mesothelioma.

The question of a comparison between carbon nanotubes and asbestos arises for several reasons. Some varieties of carbon nanotubes are similar in shape to asbestos fibers, and like asbestos, some varieties of carbon nanotubes have been shown in laboratory studies to persist in the lungs of laboratory animals. Some animal studies have even shown effects similar to those of asbestos.

Carbon nanotubes are tiny, cylindrical, manufactured forms of carbon. There is no single type of carbon nanotube. One type can differ from another in terms of shape (single-walled or multi-walled) or in chemical composition (pure carbon or containing metals or other materials). Carbon nanotube exposures can potentially occur not only in the process of manufacturing them, but also at the point of incorporating these materials into polymer composites, medical nanoapplications, and electronics.

The release of two recent reports, one from a research lab in Japan (Takagi et al., J Toxicol Sci 33:105-116, 2008) and one—this week—from the United Kingdom (Poland et al., Nature Nanotechnology advance online publication, 20 May 2008;[DOI10.1038/nnano.2008.111]) contribute to the carbon nanotube/asbestos fiber comparison debate. The publication of the Japanese study contributed to the decision by the Japanese Ministry of Health, Labor and Welfare to issue a notice which instructs those involved in the manufacture, repair and inspection of nanomaterials that the processes should be carried out under either sealed, unattended or automated conditions, or a local exhaust system should be installed.1, 2, 3 The recently published British study adds to the body of work showing an asbestos-like response (more below).

What are the implications of the most recent finding to the risk assessment and risk management of carbon nanotubes in U.S. workplaces?

The question of whether carbon nanotubes pose a toxicological hazard has been investigated since at least 2003. A challenge has been in determining if carbon nanotube materials used in the workplace have the same characteristics as those associated with biological responses in laboratory studies. Earlier studies used materials with high levels of other forms of carbon such as carbon black and high levels of metal catalyst.

Carbon nanotubes can vary widely in diameter, length, number of layers, and structures. They can also vary widely in surface composition, since certain carbon nanotubes may be “coated” with specific metals or other materials in order to perform specific functions. Also, they can clump together or agglomerate, which can affect their potential for settling in the lungs if inhaled, their ability to penetrate the body’s membranes and consequently move from the lungs to other organs, and their interaction with cells and tissue. Such variations bring an additional degree of complexity to risk assessment analysis for carbon nanotubes.

In 2005, NIOSH researchers showed that aspiration of single-walled carbon nanotubes in mice caused progressive fibrosis and granuloma formation.4 (Fibrosis and granuloma reduce gas-exchange area in the lung, thus making breathing difficult.) It is estimated that one month of exposure to carbon nanotubes at the airborne concentration of 5 milligrams per cubic meter of air, or mg/m3, would yield an equivalent dose in workers to that causing fibrosis in the mouse.5 The 5 mg/m3 concentration is sometimes reported on material safety data sheets as a manufacturer’s suggested exposure limit for carbon nanotubes and is based on the permissible occupational exposure limit (PEL) for graphite, whose most commonly known use is as a powder for manufacturing pencils. However, the findings reported by NIOSH in 2005 suggest that, on the basis of the effects seen in the laboratory studies, it might not be appropriate to use the graphite PEL for carbon nanotubes. In fact, BSI British Standards Published Document PD 6699-2:2007 “Guide to safe handling and disposal of manufactured nanomaterials” suggests setting a benchmark exposure limit for nanoscale fibers longer than 5 µm to one tenth of the PEL for asbestos, that is at 0.01 fiber per cubic centimeter. However, this benchmark exposure limit, described as a “pragmatic guidance level only,” was not rigorously developed and is derived “on the assumption that the hazard potential of the nanoparticle form is greater than the large particle form.”

This weeks’ British study finds that long (that is, longer than 20 micrometer or µm) multi-walled carbon nanotubes exhibit asbestos-like response in the form of injury to the linings of the body cavity in laboratory mice, while short and tangled multi-walled carbon nanotubes do not. A multi-walled carbon nanotube is composed of several nanotubes on a common axis. The Japanese study reports that multi-walled carbon nanotubes were more potent in causing mesothelioma than asbestos in laboratory mice genetically modified to be prone to cancer.

Asbestos-like responses to carbon nanotubes may not be entirely surprising to scientists, given previous toxicological and epidemiological studies of other biopersistent fibers since such studies show that once fibers are deposited in the lung, they stay there.6 However, questions have been raised about using these research findings for risk assessment analysis in the light of study limitations such as use of model animals, artificial administration methods, and sometimes extremely high doses, which are not representative of those exposures usually present in the workplace environment. Such limitations are not unusual for pioneering scientific studies. They simply mean that at this stage of the research, gaps remain that need to be closed by further study before quantitative risk assessment can be conducted.

How do we protect workers today?

In the workplace, developing and implementing a workplace risk management program (including evaluating the hazards, assessing worker exposures, installing and evaluating engineering controls, establishing procedures for personal protective equipment, and providing worker education and training programs) can minimize worker exposure to carbon nanotubes. NIOSH recommends that such prudent practices be used while scientists continue the research that is needed for better risk assessment. (See NIOSH Approaches to Safe Nanotechnology.) Use of basic engineering control systems such as enclosures and local exhaust ventilation was shown to greatly reduce exposure levels, while filters used in HVAC systems and respirators were reported to capture nanoscale particles with stated levels of efficiency.7 In addition, medical screening is part of a complete safety and health management program, and established medical surveillance approaches can help to assess whether control measures are effective and identify new or unrecognized problems and health effects.8

While the mechanisms of biological responses to carbon nanotubes are not yet fully understood, recent studies such as those from Japan and the UK add to the growing body of peer-reviewed scientific literature and remind the occupational safety and health community that carbon nanotubes should be handled prudently to minimize potential exposures in the workplace and to prevent potential adverse health effects in workers.

—Vladimir V. Murashov, Ph.D.

Dr. Murashov is a Special Assistant for Nanotechnology to the NIOSH Director. He is a member of the U.S. Nanoscale Science, Engineering, and Technology subcommittee. He also leads projects for the ISO Technical Committee 229 (Nanotechnologies) and the Organization for Economic Cooperation and Development’s Working Party on Manufactured Nanomaterials.

26 comments on “Nanotechnology: Should carbon nanotubes be handled in the workplace like asbestos?”

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This study does not consider the nature of the catalysts incorporated into the body along with the tubes. The catalysts used in this partiular study were, for some reason, nickel, cobalt and combinations of nickel with cobalt. Nanotubes both mulitwall or single wall can be grown with iron catalysts so these was not necessary inclusions. Since nickel and cobalt are both known to cause a very strong mutagenic reponse perhaps this is what they were seeing. In addition it is well known that CNTs can have adsorbed high molecular weight hydrocarbons some of which also will cause a mutagenic response. THis is also true of other forms of carbon unless special means are used to remove these species. Aside from these two effects, the electronic nature of CNTs is related to their Chirality, again this was not a controlled variable.

We have limited experience with measurements in a nanotube production facility. We measure very low concentrations (expressed as a surface area per unit volume)in the fraction below 1 µm. I suspect coagulation of the tubes in the vortex of the cyclone.

We intend to sample a coarser fraction (still in the respirable range). This coagulation would suggest that similar processes would occur in the respiratory system??

From a chemical point of view carbon nano-tubes are part of the family of polycyclic aromatic condensed rings (see Polycyclic aromatic hydrocarbons (PAHs) at [http://en.wikipedia.org/wiki/Polycyclic_aromatic_hydrocarbon] ). These molecules are able to form stable “radicals” that can chemically “interact” with DNA and are capable of altering the chemical structure of DNA promoting DNA miss-functioning and cancer formation (see for ex. Benzopyrene [http://en.wikipedia.org/wiki/Benzopyrene]). Polycyclic aromatic hydrocarbons are formed during the synthesis of CNTs and are “absorbed” on the internal and external surfaces of the nano-tubes. These substances can be released when CNTs came in contact with human body. Also directly CNTs are able to for”very stable radicals” that could interact with DNA. More deep investigations are needed before use CNTs on a large scale.

Agglomeration of carbon nanotubes can occur as they move in the air including air in the lung. Nanotube agglomeration can affect their potential for settling in the lungs if inhaled, their ability to penetrate the body’s membranes and consequently move from the lungs to other organs, and their interaction with cells and tissue.

NIOSH is the United States government agency with legislative responsibility to recommend occupational health standards to OSHA. Without a REL, this post is of minimal value to practitioners.

The post is also deficient for failing to note that laboratory bioassays of carbon black provide clear evidence of carcinogenicity, that IARC has found sufficient evidence in laboratory studies that carbon black is carcinogenic, and therefore classified carbon black as possibly carcinogenic to humans, group 2A. NIOSH has a responsibility to opine whether carbon nanotubes are at a minimum carbon black, and whether the bioassay and IARC designation must be disclosed on MSDS of materials containing > .1% carbon nanotubes.

Thank you for your comment. NIOSH is exploring the development of Recommended Exposure Limits (RELs) for carbon nanotubes and will request information on the topic from the public in the near future. Carbon particles need to be treated on a case by case basis. One type of carbon material does not predict how another material will behave regarding carcinogenicity. Hence, they most likely should be considered separately when developing RELs. For example, as mentioned in the blog, data on graphite (a carbon polymorph) may not be applicable to carbon nanotubes.

Concerning Nanotechnology: With its medical aplication and its ability to monitor the human body, is it detectable with a simple blood test? If not, what type would be required? If your agency is not able to answer this question, where would I be able to find this answer? My question is derived from personal research and an airing from the ABC Today show. The airing of this show was the week of nov. 5th to nov 12th 2007

NIOSH is the federal agency responsible for conducting research and providing guidance to protect workers from risks they face on the job. NIOSH is carrying out a program of research on nanotechnology applications to be able to make science-based recommendations to protect workers who manufacture or use nanomaterials on their job. NIOSH believes that answers to the following occupational questions are essential to understanding these implications and applications:

◦How might workers be exposed to nano-sized particles in the manufacturing or industrial use of nanomaterials?
◦How do nanoparticles interact with the body’s systems?
◦What effects might nanoparticles have on the body’s systems?
However, NIOSH has not conducted specific research on biomonitoring for engineered nanomaterials, such as conducting blood tests for engineered nanoparticles.

Other agencies that may be able to address your question on blood tests for nanomaterials are:

My brother aged just 50 died as a result of working in the electronics industry sinse the early 80’s. He had been diagnosed as having multiple myeloma with solitary plasmacytoma {volcano like massive swelling protruding out of the back of his head) one of the most degenerative and debilitating diseases I have ever come across,which affects the blood, immune system kidneys and bone marrow. BIOMONITORING should be paramount and a legality.

What is the Health risk of Nanotubes if inhaled? Nanotechnology is a rapidly advancing industry with many new products already available to the public. Therefore, it is essential to gain an understanding of the possible health risks associated with exposure to nanomaterials and to identify biomarkers of exposure. In humans and in other living organisms, they may move inside the body, reach the blood and organs such as the liver or the heart, and may also cross Cell membranes.

Inhaled nanoparticles can deposit in the lungs and then potentially move to other organs such as the brain, the liver, and then spleen possibly the foetus in pregnant women. Some materials could become toxic if they are inhaled in the form of nanoparticles. Inhaled nanoparticles may cause lung inflammation and heart problems.

My question is how safe is clothing that uses nano technology to give the clothing a spill proof property. I have been doing some reading on nanotechnology, it seems to be very wide spread, covering many different processes and use. Is there any information out there on how safe this is when used on our clothing?

The County currently has firms researching nanotechnology in the County. From a wastewater pretreatment view, how do I inspect these facilities without being exposed, what methods are available to remove nanoparticles from wastewater, how do we prevent wastewater treatment operators from exposure, and will these nanoparticles pass through the treatment process potentially impacting the receiving stream? Since nano products are already on the market (clothing, sun tan lotion, cosmetics)they are entering the wastewater. Will they be harmful to our micororganisms?

The NIOSH web-based document, ‘Approaches to Safe Nanotechnology: An Information Exchange with NIOSH,’ which is available at http://www.cdc.gov/niosh/topics/nanotech/safenano/, provides general interim recommendations for controlling work-related exposures to nanoparticles. You and your management may wish to consult the document to determine how to apply the recommendations to meet your concerns.

The two studies above seem to indicate that the development mesothelioma is no longer unique to asbestos exposure. If these studies can replicated , workplace exposures should be evaluated for nanoparticles, and exposure limits should be developed based on both graphite and on asbestos exposure limits. This is due to the fact that any OEL’s developed must take into account the fiber-like quality of the nanoparticles as well as the carcinogenicity of the carbon itself. I believe that OSHA should develop recommended exposure limits as they are relevant, and very necessary given the information presented above.

Studies Combine to Show Palladium Catalytic Converter Particle cracking Causes Increased Health Risk. Not only workers but the entire public need protection from insoluble linear crystalline nano-particles and carbon nano-lens particles i.e. carbon fibers, nanotube fibers, asbestos and thin edged insoluble crystalline convex lens shaped nano-particles. In relation to the cell plasma membrane with a thickness of about 7 nm, were the particle point or edge thickness, modulus, and insolubility give cause to cell irritation by puncture, cutting, scraping or scratching sometimes accompanied by additional chemical irritation. Any insoluble particle that presents a point or cutting edge capable of puncturing or cutting the cell plasma membrane with the aid of normal body motion will present the same low-grade (slow development) hazards as asbestos. The smaller and sharper the particle, down to 7 nm, the greater the potential for per particle harm. Carbon nanotubes, and carbon nanotube fragments as short as 7 nanometers can puncture the cell plasma membrane resulting in possible cell necrosis. The number of puncture points and cutting edges is the critical factor not the mass of the particles. Independent Carbon nanotube fragments 1 to 8nm in diameter and 7nm to 800nm in length can kill one cell at a time until disposed from the organism.

The greatest use of catalytic converters, which can produce CNT’s since 1975 in CA. and 1979 in the U.S. is in the automobile industry.

An Immediate government investigation of catalytic converter use is warranted. By 1979 the Environmental Protection agency had imposed catalytic converters on industry and spark ignition engine cars, this has created an increase of Blue carbon particles in the atmosphere by 100’s of times. Government is the cause of carbon problems not the people or industry. The multiplication of Blue Carbon to over 10,000% more particles from the car per cubic meter of exhaust into the atmosphere since 1979 is Hegemo-genous (Government caused). A 17 to 20% increase in CO2 production from the engine/catalytic converter system and a 10% decrease in mileage efficiency also resulted from mandatory catalytic converters, resulting in an accumulative 27 to 30% increase in CO2 emissions from cars. The Small engine, excellent milage, cars of the 1970’s, like the simple efficiency of the Datsun 500, had to up size the engine, add fuel injection, and electronic ignition control, to accommodate the catalytic converter requirements. These required changes with the catalytic converter, cut mileage from 40 mpg to the low 30’s.

Car companies to accommodate the increased cost of government mandates added comfort, convenience, and luxury items to make the higher prices palatable to the consumer. The total effect brought mileage down into the 20-28 mpg range and costs up from the sub $5,000’s to over $10,000 and on to $30,000 plus.

In 1979 the diesel trucking industry developed and used a industry produced tractor-trailer sized mobile particle counter to test the effectiveness of catalytic converters for diesel carbon particulate control. The result showed diesel engines produced up to 100 times more particles (note: this test equipment undercounted sub 50 nm particles) and catalytic converter poisoning resulted from the high carbon content of diesel fuel. Catalytic converters were deemed ineffective to control air pollution from diesel engines. No agency of the Federal Government deemed it necessary to reevaluate the use of catalytic converters for spark ignition engines from the results of this study.

In 1980 an auto industry laboratory study of spark-ignition engines found the multiplication of exhaust particle counts during the catalytic converter process.
(Heywood John B., Keck James C., Rife Joe, January 1980; HYDROCARBON FORMATION AND OXIDATION IN SPARK-IGNITION ENGINES Final Report on a Research Program Funded by General Motors Research Laboratories)

Multiple studies since then have confirmed the multiplication effect of palladium catalytic converters on the number of particles. No agency in the Federal Government deemed it necessary to reevaluate the use of catalytic converters for spark ignition engines from the results of these studies. In 1980, At lest one Aero-space carbon fiber expert wanted to inform air quality officials of possible risks from cracking hydrocarbons with a palladium catalyst but was blocked by the secret security status of carbon fiber production.

In 1985 Robert Curl, Harold Kroto and Richard Smalley at the University of Sussex and Rice University, published a scientific paper on the manufacture of “fullerene” believing they had discovered a way to manufacture pure carbon nano molecules using palladium catalytic conversion. ([http://en.wikipedia.org/wiki/Fullerene]) By 2001 the use of palladium catalytic converters in the production of carbon nano-tubes and carbon nano-particles had become common knowledge in materials science engineering.

In 2004 The first open to the public toxicology study of carbon nanotubes (CNT’s) was published. Since this fist public study at lest 63 public toxicology studies have been released on CNT’s.
Wang H, Wang J, Deng X, Sun H, Shi Z, Gu Z, Liu Y, Zhao Y: Biodistribution of carbon single-wall carbon nanotubes in mice. J Nanosci Nanotechnol 2004, 4:1019-1024.

[Tables 4 and 5 from the study cited above were included in the original comment, but were omitted from this comment due to space constraints]

Steep increases in cardiovascular operations to median age trends, growth, and aging of the population indicates a rapid nation wide increase in a hazardous material exposure and/or life style-health degradation on a massive scale. The evidence points to Insoluble Carbon nano-particles mostly less than 100 nanometers in size. Carbon nano-tube fragments with a particle length less than 100 times the diameter of the nano-tube being the most hazardous. These particles are not chemically active but physically puncture very small wounds in cell plasma membranes and other membranes of the body. They cause the immune system response of scar tissue formation to heal these small wounds within the alveolar of the lungs, arteries, other circulatory systems and membranes of the body.

By 2006 an addditional 1.2 million of the U.S. population per year were requiring cardiovascular medical operations and procedures, above expected levels. Adding the procedures together, Between 1979 and 1985, something wrong grew to a steep upward trend in only 6 years, and has continued to worsen on this increasing trend. Only a tremendous improvement in medical interventions has keep this from becoming a massive life and death/heath disaster.
Source: NCHS, NHLBI, U.S. Census and AHA

The trend in Pacemakers equates to an index of procedures to growth, median age increase, and aging of the population.

U.S. Total Population growth gives an index to population growth over the period.

The history of asbestos as we know it dates back 2000 years. It was the Greeks who named this mineral asbestos, meaning inextinguishable. The ancient Greeks observed the harmful biological effects but continued to use the mineral said to have magical properties. Pliny (Roman naturalist) and Strabo (Greek geographer) noted an appearance of “sickness of the lungs” in slaves who wove asbestos into cloth. The Greeks also used asbestos for the wicks of the eternal flames of the vestal virgins, as the funeral dress worn by kings and for napkins. They were so impressed with the magical properties of the mineral that they were willing to overlook its harmful symptoms for humans. They went as far as calling asbestos “amiantus”, meaning “unpolluted”.

Hi!
Very interesting information about carbon nanotubes.I didn’t know past that NIOSH researchers showed that aspiration of single-walled carbon nanotubes in mice caused progressive fibrosis. These researchers are very good and do always some kind of amazing things. \
Thanks for sharing this information.

My Father died of asbestos I don’t know too much about nanotechnology, but this was a very interesting read. I just hope that before any of this can potentially hurt anyone in the work place they research the potential risks and the workplaces to ensure no one will die like my father.
Thanks for sharing this information.

Nano technology in all forms is a relatively new concept for the whole world. It is yet to be proven whether these Nano particles actually affect human beings, although there is a huge possibility that it can do some major damage. Unless some scientifically proven result comes out, ambiguity regarding the issue will always remain.

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